In honor of 4/20, the unofficial marijuana holiday that falls on April 20, CNBC's Jim Cramer took a look at the state of the red-hot bull market in marijuana.

"[It's] the hottest sector of the economy that remains totally illegal according to the federal government," the "Mad Money " host said on Friday.

So far, 29 U.S. states and Washington, D.C. have legalized medical marijuana, and nine states and D.C. have legalized recreational marijuana. As related businesses in those states flourish, they have also created new ways to invest in the marijuana industry.

"So while I may not be a cannabis connoisseur ... and I don't know the best way to tell you to get baked, I can absolutely help you figure out how to play the booming bud industry," Cramer said.

But even as marijuana investing grows in popularity — research firm Cowen estimates that the U.S. cannabis market could be worth $75 billion by 2030 — Cramer wasn't sold on the trend.

"The issue is that there's been a huge, cryptocurrency-like run in this group and it's making most of these stocks too expensive for my taste," the "Mad Money" host said.

Even so, Cramer acknowledged the legitimacy of the marijuana business. Numerous studies have touted the benefits of medicinal marijuana, and the Food and Drug Administration will soon weigh the approval of the first cannabis-derived drug on the U.S. market.

Lawmakers are also turning positive on the plant. On Thursday, Senate Minority Leader Chuck Schumer announced a plan to decriminalize marijuana on the federal level.

Last week, former Speaker of the House John Boehner announced he would join the advisory board of privately-held marijuana company Acreage Holdings, telling CNBC in a statement that his "thinking on cannabis has evolved."

"Of course, the Trump administration has very different views, especially our very old-school Attorney General [Jeff Sessions], " Cramer said. "Sessions is not a fan of the marijuana industry and that makes investing in these stocks inherently more risky than investing in something that's less legally murky."

At this point, most marijuana companies are based in Canada, where medical marijuana is federally legal and recreational legalization is on its way.

But most of their stocks trade "over the counter," which Cramer said makes them illiquid, highly volatile and too risky for him to recommend.

He pointed to three Canadian marijuana growers: Aurora Cannabis Company, Canopy Growth Corp. and Aphria. With the rise of marijuana-themed exchange-traded funds, or ETFs, all of their stocks have soared to "extreme" valuations, Cramer said.

Experts estimate that the Canadian market could be worth $9 billion in several years. But Aurora, Canopy and Aphria are currently worth $3.8 billion, $4.7 billion and $1.85 billion, respectively, all "very optimistic" valuations considering the research at hand, Cramer said.

"Here's the thing: legalization is horrible for pot pricing," the "Mad Money" host said. "When states legalize, prices fall through the floor. I mean, it's a plant, for heaven's sake. The fact that it's against the law is the only thing that makes it expensive, so if you're betting on the state of the industry several years down the line, you really should bake that into your numbers."

Cramer wasn't even sure about the seemingly stable Cronos Group, a diversified international cannabis producer with the first pot stock to be listed on a major U.S. exchange.

"It's too risky for me to recommend to you," he said, noting that the company only generated less than $5 million in revenue in 2017 but its stock is currently valued at $1.3 billion.

For investors seeking some green, Cramer recommended the stocks of British drug company GW Pharmaceuticals, which develops cannabis-derived medications, and Constellation Brands, an alcohol company with a nearly 10 percent stake in Canopy Growth.

"The bottom line? When you're dealing with a controlled substance, you always need to play it safe," Cramer concluded. "So when it comes to investing in the marijuana stocks, most of them are way too dank for me. They're downright bubblicious, which is why only GW Pharma and Constellation Brands have my blessing because I don't want your money to go up in smoke."